1. Field of the Invention
The present invention relates to a semiconductor manufacturing technology. More specifically, the invention relates to a plasma processing apparatus that attracts a substrate by an electrostatic force and a plasma processing method using the plasma processing apparatus.
2. Description of the Related Art
In a plasma processing apparatus for forming a thin film or performing plasma etching in a semiconductor manufacturing process, an electrostatic chuck is used as equipment that holds a processed substrate (hereinafter, simply referred to as a substrate), such as a semiconductor wafer in a predetermined position. Since the electrostatic chuck may generate an attractive force over an entire rear surface of the substrate, a temperature controlling function such as a heater or a cooling device is provided in the electrostatic chuck and thus a substrate stage having an excellent temperature control property can be realized.
However, in the electrostatic chuck, even after a voltage application is stopped, it is difficult to separate the substrate from the electrostatic chuck due to the charge remaining on the substrate. Particularly, this phenomenon is important in the electrostatic attracting stage using Johnson-Rahbeck effect, which is employed in most of electrostatic chucks, since a large attractive force can be obtained with a low voltage. The Johnson-Rahbeck effect is to obtain a large attractive force by allowing minute current to flow through an interface between the surface of the electrostatic chuck and the substrate to store a large amount of charge in a narrow gap of the interface. That is, by storing the charge in the gap of the interface or the substrate, a large attractive force can be realized. However, it is difficult to separate the substrate from the electrostatic chuck when the remaining charge is not removed.
With respect to this phenomenon, various solutions have been conventionally suggested. A method of applying a voltage reverse to a voltage at the time of attraction to remove the charge remaining on the semiconductor wafer was suggested. This method is generally known as a remaining charge removing method (for example, see Japanese Unexamined Patent Application Publication No. 11-330217).
Furthermore, a method of bringing a grounded conductor into contact with a semiconductor wafer and allowing charge to escape to separate the semiconductor wafer from an electrostatic chuck was suggested (for example, see Japanese Unexamined Patent Application Publication No. 2002-83860). In addition, a method of applying an AC voltage to an electrostatic chuck and a method of ejecting inert gas on a surface between a semiconductor wafer and a surface of a chuck to separate the semiconductor wafer from the chuck are known.
However, according to the method of applying the reverse voltage to the substrate disclosed in Japanese Unexamined Patent Application Publication No. 11-330217, it is difficult to set a value of the applied voltage or an applying time. That is, in this method, since the reverse voltage is applied to the substrate, an attraction force due to the reverse voltage may likely be generated. In Japanese Unexamined Patent Application Publication No. 11-330217, by obtaining a condition that the remaining quantity of reverse charge becomes zero in each electrostatic chuck, this problem was avoided. However, since the substrate itself is a portion of an electrostatic attracting circuit at the time of the actual use, the condition that the remaining quantity of charge becomes zero is affected by a film kind or a film structure of the substrate. That is, in this method, when the condition that the remaining quantity of charge becomes zero is obtained by only the electrostatic chuck, an optimal value for separating the substrate may not be obtained.
Next, according to the method of directly grounding the substrate to allow the charge to escape disclosed in Japanese Unexamined Patent Application Publication No. 2002-83861, since the wafer of the substrate is stripped by a mechanical force, it is impossible to completely remove the possibility of deviation or cracking of the wafer. Conventionally, in the electrostatic attracting stage of the plasma processing apparatus, the attracting condition is set to the voltage and the voltage is set to a constant value regardless of a kind of the substrate. As disclosed in Japanese Unexamined Patent Application Publication No. 11-330127, an optimal value is obtained in each electrostatic chuck stage. That is, research to obtain an optimal value for an individual difference of the electrostatic chuck stage has progressed, but electrical characteristics such as resistance of the substrate itself has not been considered.